Precursor compositions for an insulation and insulated rocket motors

ABSTRACT

A precursor composition comprising, before curing, ethylene propylene diene monomer (EPDM), zinc oxide, silica, polymerized 1,2-dihydro-2,2,4-trimethylquinoline, a solid chlorinated paraffin, stearic acid, a five carbon petroleum hydrocarbon, trimethylolpropane trimethacrylate, and a peroxide. A rocket motor including a reaction product of the precursor composition and a method of insulating a rocket motor.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.15/461,339, filed Mar. 16, 2017, pending, the disclosure of which ishereby incorporated herein in its entirety by this reference.

TECHNICAL FIELD

Embodiments of the disclosure relate to a precursor composition of aninsulation for use in an article and to methods of insulating thearticle. More particularly, embodiments of the disclosure relate to aprecursor composition for an insulation for use in various locations onrocket motors or other articles and methods of insulating a rocket motoror other article.

BACKGROUND

Rocket motors include a case that houses an energetic fuel, which mayalso be characterized as a propellant. An insulation and an optionalliner protect the case interior from thermal and erosive effects ofparticle streams generated by combustion of the energetic fuel orpropellant. The rocket motor includes a nozzle operatively associatedwith the case to receive combustion products generated by combustion ofthe propellant and to expel the combustion products, generating thrustto propel the rocket motor and associated aerospace vehicle. Theinsulation is bonded to an interior surface of the case and isfabricated from a composition that, upon curing, is capable of enduringthe extreme temperature, pressure, and turbulence conditions producedwithin the case. High temperature gases and erosive particles areproduced with the case during combustion of the energetic fuel orpropellant. During use and operation, the temperatures inside the casemay reach about 2760° C. (about 5000° F.), pressures exceed about 1500pounds per square inch (“psi”) (about 10.3 MPascal), and velocities ofgases reach or exceed Mach 0.2. These conditions, along with arestrictive throat region provided along a passageway between the caseand the nozzle, combine to create a high degree of turbulence within thecase. In addition, the gases produced during combustion of the fuel orpropellant contain high-energy particles that, under a turbulentenvironment, erode the insulation. Additionally, if the fuel orpropellant penetrates through the insulation, the case may melt, beeroded, or otherwise be compromised, causing the rocket motor to fail.

Depending on the configuration of the rocket motor, various combinationsof mechanical, thermal, and ablative properties are desired in differentsections of the rocket motor. For some sections, high elongationproperties are desirable while for other sections, good ablation and/orgood mechanical properties are desirable. Some sections need goodelectrostatic discharge (ESD) properties, while other sections need goodinsulative properties. To provide the desired properties, conventionalrocket motors employ different insulations on different sections of thecase. However, the use of the different insulations adds to the cost andcomplexity of manufacturing the rocket motor.

BRIEF SUMMARY

Disclosed is an embodiment of a precursor composition comprising, beforecure, ethylene propylene diene monomer (EPDM), zinc oxide, silica,polymerized 1,2-dihydro-2,2,4-trimethylquinoline, a solid chlorinatedparaffin, stearic acid, a five carbon petroleum hydrocarbon,trimethylolpropane trimethacrylate, and a peroxide.

A rocket motor is also disclosed and comprises a case, an insulation onat least a portion of the case, and a propellant in the case. Theinsulation comprises a reaction product of ethylene propylene dienemonomer (EPDM), zinc oxide, silica, polymerized1,2-dihydro-2,2,4-trimethylquinoline, a solid chlorinated paraffin,stearic acid, a five carbon petroleum hydrocarbon, trimethylolpropanetrimethacrylate, and a peroxide.

A method of insulating a rocket motor is also disclosed. The methodcomprises applying a precursor composition of an insulation to at leasta component of a rocket motor and curing the precursor composition toform the insulation. The precursor composition comprises ethylenepropylene diene monomer (EPDM), zinc oxide, silica, polymerized1,2-dihydro-2,2,4-trimethylquinoline, a solid chlorinated paraffin,stearic acid, a five carbon petroleum hydrocarbon, trimethylolpropanetrimethacrylate, and a peroxide.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a rocket motor including aninsulation formed from a precursor composition according to anembodiment of the disclosure;

FIG. 2 is an enlarged view of the portion of the rocket motor encircledin

FIG. 1;

FIG. 3 is a photograph showing the flow properties of an insulationaccording to an embodiment of the disclosure in a spider mold;

FIG. 4 is a photograph showing the extrusion properties of a precursorcomposition of the insulation according to an embodiment of thedisclosure;

FIG. 5 is a bar graph showing weight loss (percent weight loss) from aseventy pound char (SPC) motor test of low, mid, and high sections ofthe char motor having insulation formed from the precursor compositionaccording to an embodiment of the disclosure compared to twoconventional, silica-filled EPDM insulations;

FIG. 6 is a plot of the material ablation rate (mm/s) versus chamberlocation (inches) of the insulation formed from the precursorcomposition according to an embodiment of the disclosure from the low,mid, and high sections of the SPC motor test compared to twoconventional, silica-filled EPDM insulations; and

FIG. 7 is a bar graph showing the average material ablation rate (mm/s)of the insulation formed from the precursor composition according to anembodiment of the disclosure from the low, mid, and high sections of theSPC motor test compared to two conventional, silica-filled EPDMinsulations.

DETAILED DESCRIPTION

An insulation including a polymer of ethylene propylene diene monomer(EPDM) is disclosed. When used to insulate a rocket motor or otherarticle to be insulated, the insulation may be characterized as“universal” in that the same insulation may be used on different regionsof the particular rocket motor or article that require insulation. Theuniversal insulation is formulated to protect different regions of therocket motor or article that need protection from one or more of heat,erosion, and other extreme conditions experienced during use andoperation of the rocket motor or other article. The universal insulationmay be used as internal insulation of the rocket motor or other article,external insulation of the rocket motor or other article, or as a shearply to couple a case of the rocket motor to a rocket skirt. Theuniversal insulation provides improved or comparable mechanical,physical, rheological, thermal, and ablative properties compared toconventional, silica-filled EPDM-based insulations. By using a singleinsulation, the cost and complexity of manufacturing the rocket motor orother article is reduced.

A precursor composition of the insulation includes the EPDM, anantioxidant, one or more fillers, a flame retardant, a processing aid, aplasticizer, a co-agent, and a curative. The ingredients of theprecursor composition of the insulation are commercially available.Therefore, none of the ingredients are obsolete. The precursorcomposition of the insulation may be substantially free of fibers. Asused herein, the term “precursor composition” means and includesingredients of the composition before the ingredients are reacted (e.g.,cured). Curing the precursor composition forms the insulation, which maythen be applied to the rocket motor or other article.

As used herein, the terms “comprising,” “including,” “containing,”“characterized by,” and grammatical equivalents thereof are inclusive oropen-ended terms that do not exclude additional, unrecited elements ormethod acts, but also include the more restrictive terms “consisting of”and “consisting essentially of” and grammatical equivalents thereof. Asused herein, the term “may” with respect to a material, structure,feature or method act indicates that such is contemplated for use inimplementation of an embodiment of the disclosure and such term is usedin preference to the more restrictive term “is” so as to avoid anyimplication that other, compatible materials, structures, features andmethods usable in combination therewith should or must be excluded.

The illustrations presented herein are not meant to be actual views ofany particular device, but are merely idealized representations that areemployed to describe the present disclosure. The figures are notnecessarily drawn to scale. Additionally, elements common betweenfigures may retain the same numerical designation.

The EPDM is a terpolymer of ethylene, propylene, and a non-conjugateddiene. The non-conjugated diene may include, but is not limited to,ethylidene norbornene (ENB). The EPDM may have a diene content of fromabout 1% by weight (wt %) to about 10 wt %, such as about 5.0 wt %. Inone embodiment, the EPDM has a diene content of about 5.0 wt %. The EPDMmay have an ethylene content of greater than about 40 wt %, such asbetween about 40 wt % and about 85 wt %, between about 40 wt % and about75 wt %. In one embodiment, the EPDM has an ethylene content of about 50wt %. The EPDM may be commercially available from Dow Chemical Company(Midland, Mich.) under the NORDEL® tradename. By way of example only,the EPDM may be NORDEL® IP 4520. The EPDM may be present in theprecursor composition of the insulation at from about 70 parts to about150 parts. In one embodiment, the EPDM is NORDEL® IP 4520, has a dienecontent of about 5.0 wt %, an ethylene content of about 50.0 wt %, andis present in the precursor composition of the insulation at about 100parts.

The antioxidant may be a hydroquinoline compound, such as a polymerized1,2-dihydro-2,2,4-trimethylquinoline, which is commercially availablefrom Vanderbilt Chemicals, LLC (Norwalk, Conn.) under the AGERITE®tradename. One or more antioxidants may be used. By way of example only,the antioxidant may be AGERITE® Resin D. The antioxidant may be presentin the precursor composition of the insulation at from about 0.35 partto about 0.75 part. In one embodiment, the antioxidant is AGERITE® ResinD, a polymerized 1,2-dihydro-2,2,4-trimethylquinoline, and is present inthe precursor composition of the insulation at about 0.5 part.

The filler may be zinc oxide, silica (silicon dioxide), or a combinationthereof. The zinc oxide may include, but is not limited to, a propionicacid coated zinc oxide having a surface area of from about 4.0 m²/g toabout 6.0 m²/g and a particle size of from about 0.18 μm to about 0.27μm, such as Zoco 627, which is commercially available from Zochem Inc.(Brampton, Canada). The silica may be an amorphous, precipitated silica,such as that commercially available from PPG Industries, Inc.(Pittsburgh, Pa.) under the HI-SIL® tradename. By way of example only,HI-SIL® 233 silica having a surface area (BET) of 135 m²/g may be usedas the filler. In one embodiment, the filler includes Zoco 627, the zincoxide, and HI-SIL® 233, the amorphous, precipitated silica. The zincoxide may be present in the precursor composition of the insulation atfrom about 2.1 parts to about 4.5 parts and the amorphous, precipitatedsilica may be present in the precursor composition of the insulation atfrom about 21 parts to about 45 parts. In one embodiment, the zinc oxideis present in the precursor composition of the insulation at about 3parts and the amorphous, precipitated silica is present in the precursorcomposition of the insulation at about 30 parts.

The flame retardant may be a solid chlorinated paraffin, such as thatcommercially available from Dover Chemical Corporation (Dover, Ohio)under the CHLOREZ® tradename. The solid chlorinated paraffin may be a70% chlorinated paraffin, such as CHLOREZ® 700. The solid chlorinatedparaffin may be present in the precursor composition of the insulationat from about 4.2 parts to about 9 parts. In one embodiment, the solidchlorinated paraffin is present in the precursor composition of theinsulation at about 6 parts.

The processing aid may be a fatty acid or fatty acid derivative, such asthat commercially available from PMC Biogenix, Inc. (Memphis, Tenn.)under the INDUSTRENE® tradename. The fatty acid may be a stearic acid(C₁₇H₃₅CO₂H), such as INDUSTRENE® B. The stearic acid may be present inthe precursor composition of the insulation at from about 0.35 part toabout 0.75 part. In one embodiment, the stearic acid is present in theprecursor composition of the insulation at about 0.5 part.

The plasticizer may be an aliphatic resin, such as that commerciallyavailable from TOTAL Cray Valley (Exton, Pa.) under the WINGTACK®tradename. The aliphatic resin may be a five carbon (C5) petroleumhydrocarbon, such as WINGTACK® 95. The aliphatic resin may be present inthe precursor composition of the insulation at from about 4.2 parts toabout 9 parts. In one embodiment, the aliphatic resin is present in theprecursor composition of the insulation at about 6 parts.

The co-agent may be a low volatility trifunctional monomer, such astrimethylolpropane trimethacrylate, which is commercially available fromSartomer Americas (Exton, Pa.) as SR350. One or more co-agents may beused. The co-agent may be present in the precursor composition of theinsulation at from about 5.6 parts to about 12 parts. In one embodiment,the trimethylolpropane trimethacrylate is present in the precursorcomposition of the insulation at about 8 parts.

The curative may be a crosslinking peroxide, such as that commerciallyavailable from Arkema Inc. (Exton, Pa.) under the LUPEROX® tradename.One or more curatives may be used. By way of example only, the curativemay be LUPEROX® 231 XL40, which is a 40% active dispersion of LUPEROX®231 (1,1-di-(t-butylperoxy)-3,3,5-trimethylcyclohexane) polymerinitiator on calcium carbonate. The curative may be present in theprecursor composition of the insulation at from about 5.6 parts to about12 parts. In one embodiment, the curative is present in the precursorcomposition of the insulation at about 8 parts.

While specific examples of the antioxidant, co-agent, and curative areprovided above, other antioxidants, co-agents, and/or curatives may beused depending on the desired shelf life of the uncured precursorcomposition or of the insulation or the desired mechanical properties ofthe insulation. The antioxidant may be selected depending on whether theprecursor composition is to have an increased or decreased shelf life.Other co-agents and curatives may be selected depending on the desiredmechanical properties of the insulation.

The precursor composition of the insulation may, optionally, includemultiwalled carbon nanotubes depending on the desired ESD properties ofthe uncured precursor composition or of the insulation. The multiwalledcarbon nanotubes include, but are not limited to, those commerciallyavailable from Arkema Inc. (Exton, Pa.) under the GRAPHISTRENGTH®tradename, such as GRAPHISTRENGTH® EPDM 20. GRAPHISTRENGTH® EPDM 20contains pre-dispersed multiwalled carbon nanotubes at a concentrationof 17 wt % (20 parts).

The precursor composition of the insulation may include feweringredients than conventional, silica-filled EPDM insulation, reducingthe cost and complexity of manufacturing an article including theinsulation. In one embodiment, the precursor composition of theinsulation has 13 ingredients, compared to 22 ingredients in theconventional silica-filled EPDM insulations. By including feweringredients, future obsolescence issues with the ingredients may bereduced, such as qualification costs for future materials. Theingredients may be commercially available, further reducing theobsolescence cost.

The precursor composition may be prepared by combining (e.g., mixing)the EPDM, antioxidant, one or more fillers, flame retardant, processingaid, plasticizer, co-agent, and curative in a mixer, such as an internalmixer. All of the ingredients are solid at room temperature. Theingredients are combined in the mixer to form the homogeneous precursorcomposition. Since the precursor composition does not include fibers,the precursor composition is an isotropic material having substantiallyuniform properties throughout. Shear in the mixer generates a sufficientamount of heat to soften the EPDM, enabling the homogeneous precursorcomposition to be formed without adding a solvent. Thus, the precursorcomposition may be prepared by a solvent-less process. Since no solventsare used, a solvent removal process, such as drying or solventevaporation, is not needed before curing the precursor composition toform the insulation.

The precursor composition may be shaped into its desired form, such asby extruding, calendaring, or compression molding. The precursorcomposition may exhibit a sufficiently low viscosity such that theprecursor composition has a flowable consistency before curing. As usedherein, the term “flowable” means and includes a sufficiently lowviscosity that enables the precursor composition to change shape ordirection substantially uniformly in response to heat and/or shear, suchthat the precursor composition readily flows out of a container at roomtemperature. The flow behavior and extrudability of the precursorcomposition reduces the cost of manufacturing the rocket motor becausethe precursor composition or resulting insulation may be applied to therocket motor by automated layup processes. By reducing or eliminatingmanual layup processes, the cost of manufacturing the rocket motor maybe reduced. By way of example only, the precursor composition may becalendared to a desired thickness, such as a thickness of about 0.1 inch(about 0.254 cm). Once prepared, the precursor composition may beapplied to the rocket motor or other article and cured. Alternatively,the precursor composition may be stored until use. The precursorcomposition may be used as internal insulation or external insulation ofa rocket motor, or as a shear ply depending on the configuration of therocket motor. The precursor composition may be used as a shear ply tocouple a case of the rocket motor to a rocket skirt. The precursorcomposition may be applied to the rocket motor by hand layup or byautomated layup processes.

In addition to being used as insulation in rocket motors, the insulationmay be used in other articles where protection from heat and gases isdesired. For example, the insulation may be used for heat and gasprotection in under-the-hood applications in automobiles. The insulationmay also be used in conveyor belts and in noise-damping applications inautomobile and other fields. In addition, since the insulation may beextruded, compression molded, or calendared, the insulation may be usedin routine rubber applications including, but not limited to, suchapplications as hoses, gaskets, seals, isolators and mounts, cushions,air emission hoses, and dock fenders.

Methods of applying the precursor composition to the rocket motor andcuring the precursor composition are known in the art and, therefore,are not described in detail herein. The precursor composition may beapplied to a case of the rocket motor and cured, forming the insulationon an inner surface of the case. While the curing may occur at roomtemperature (about 20° C.-25° C.), the curing may be accelerated byapplying at least one of heat and pressure as known in the art.Alternatively, the precursor composition may be applied to a mandrel,cured to form the insulation, and subsequent layers of the rocket motorformed over the insulation.

As shown in FIGS. 1 and 2, insulation 8 may be used in a rocket motor 2.The rocket motor 2 includes a case 4 produced from a rigid, durablematerial, such as a metal or composite. The case 4 houses a solidpropellant 6 that combusts to provide the thrust necessary to propel therocket motor 2. The insulation 8 is applied to an inner surface of thecase 4, and is present between the case 4 of the rocket motor 2 and thepropellant 6. An optional liner 10 may be present between the insulation8 and the propellant 6. Methods for loading the case 4 with theinsulation 8, optional liner 10, and propellant 6 are known in the artand, therefore, are not described in detail herein. Nozzle 12 isoperatively associated with the case 4 to receive combustion productsgenerated by combustion of the propellant 6 and to expel the combustionproducts, generating thrust to propel the rocket motor 2. During use andoperation of the rocket motor 2, the insulation 8 protects the case 4from heat and particle streams that are generated by combustion of thepropellant 6.

While the insulation 8 is shown as being applied to the inner surface ofthe case 4, the insulation 8 may be used on other regions of the rocketmotor 2, either internally, externally, or both. For example, theinsulation 8 may provide ablative protection to an external bulk of thecase 4 and nozzle 12. Additionally, while the insulation 8 may be usedfor insulating a solid rocket motor and other large-scale motors, theinsulation may also be used with other motors, such as biliquid, hybridand reverse hybrid motors, or with rocket motor-propelled missiles.

A method of insulating the rocket motor 2 is also described. The methodcomprises producing the precursor composition that includes theingredients described above. The precursor composition is deposited on,or applied to, the inner surface of the case 4 of the rocket motor 2.The precursor composition is subsequently cured to form the insulation8.

The precursor compositions according to embodiments of the disclosuremay exhibit comparable or improved mechanical and ablative propertiesand improved processing characteristics compared to conventional,silica-filled EPDM-based insulations. Finding a balance between goodmechanical and ablative properties and good processing characteristicshas been difficult with conventional, silica-filled EPDM-basedinsulations. To achieve the desired balance, the conventional, suchsilica-filled EPDM-based insulations have included fibers to providegood ablative properties. However, adding fibers increases the cost andcomplexity of manufacturing rocket motors that include the conventional,silica-filled EPDM-based insulations. It was surprising that theprecursor composition of the insulation provided good ablativeproperties without including fibers in the precursor composition.Therefore, the cost and complexity of manufacturing rocket motors thatinclude insulation formed from the precursor compositions is reduced.

The following examples serve to explain embodiments of the disclosure inmore detail. These examples are not to be construed as being exhaustiveor exclusive as to the scope of this disclosure.

EXAMPLES Example 1 Precursor Composition Formulations

Precursor compositions including the ingredients shown in Table 1 wereproduced.

TABLE 1 Formulation of Precursor Compositions EPDM EPDM Composition AComposition B Amount Amount Ingredient (parts) (parts) NORDEL ® IP 4520100 60.92 AGERITE ® Resin D 0.5 0.5 Zoco 672 3 3 HI-SIL ® 233 30 30CHLOREZ ® 700 6 6 GRAPHISTRENGTH ® EPDM 20 0 47.08 INDUSTRENE ® B 0.50.5 WINGTACK ® 95 6 6 SR350 8 8 LUPEROX ® 231 XL40 8 8

Each of the ingredients was commercially available and was used asreceived. The ingredients in Table 1 were added to an internal mixer andcombined to produce the precursor compositions.

Example 2 Mechanical, Physical, and Thermal Properties

The mechanical, physical, and thermal properties of the precursorcompositions described in Example 1 were determined and are shown inTable 2. The mechanical, physical, and thermal properties weredetermined by conventional techniques. The precursor compositions ofExample 1 are indicated in Table 2 as “EPDM Composition A” and “EPDMComposition B,” respectively. The properties of EPDM Compositions A andB were compared to two conventional, silica-filled EPDM compositions,which are indicated in Table 2 as “EPDM Comparative Composition C” and“EPDM Comparative Composition D.” EPDM Comparative Compositions C and Dincluded a larger number of ingredients than EPDM Composition A, andEPDM Comparative Composition D included a larger number of ingredientsthan EPDM Composition B.

TABLE 2 Mechanical, Physical, and Thermal properties of PrecursorFormulation EPDM EPDM EPDM EPDM Comparative Comparative PropertyComposition A Composition B Composition C Composition D Number of 9 1110 14 Ingredients Specific Gravity 1.05 1.08 1.02-1.08 1.04-1.07 MooneyViscosity 44.5 — 52-57 62-82 at 212° F. Tack Time (sec) 54 152  2  2-300ESD Surface 1.04 × 10¹⁷ 3.0 × 10⁵ 3.51 × 10¹⁴ — Resistivity (ohms/sq)ESD Volume 1.75 × 10¹⁵ 1.2 × 10⁸ 5.22 × 10¹³ — Resistivity (ohms · cm)Modulus (psi) 1093 2073 2073  — Stress Capability 1553 1620 1500-30001450-3000 (psi) Strain (%) 626 348 400-800 450-700 Propellant Compatible— Compatible Compatible Compatibility Permeability Non-Permeable —Non-Permeable Non-Permeable at 20% Strain Coefficient of 197-215 —145-228 — Thermal Expansion (in/in ° F. × 10⁻⁶) ESD InsulatingESD/Conductive Insulating Insulating “—” indicates not reported

EPDM Composition A exhibited improved Mooney viscosity and tack timecompared to EPDM Comparative Compositions C and D. EPDM Composition Aalso exhibited comparable modulus, stress capability, and straincompared to EPDM Comparative Compositions C and D. EPDM Composition Awas also compatible with conventional propellants including, but notlimited to, NEPE, PBAN, and HTPB. EPDM Composition A was also determinedto be non-permeable to gases produced as volatile, combustion productsduring use of the precursor composition as insulation. EPDM CompositionB exhibited improved ESD properties compared to EPDM Composition A.

Example 3 Flow and Extrudability Properties

The rubber flow behavior of EPDM Composition A described in Example 1was determined by conventional techniques. The precursor composition wasplaced in a spider mold and cured. As shown in FIG. 3, the insulationexhibited good rubber flow characteristics in the spider mold.

The extrusion ability of EPDM Composition A was determined byconventional techniques. As shown in FIG. 4, EPDM Composition Aexhibited good extrudability. EPDM Composition A was able to be extrudedat a faster rate than the EPDM Comparative Composition C and EPDMComparative Composition D.

Example 4 Ablative Properties

The ablative properties of EPDM Composition A described in Example 1were determined in a low Mach seventy pound char (SPC) motor test. TheSPC motor test simulated conventional temperature and pressureconditions in low velocity, mid velocity, and high velocity sections ofthe char motor. The diameter of the char motor varies in these threesections, with the char motor having a relatively large diameter in thelow velocity section while in the high velocity section, the char motorhas a relatively small diameter. The diameter of the char motor at agiven location determines the amount of exposure that the insulationreceives. If the diameter is small, that section of the char motor willbe exposed to more gases and will be more prone to erosion than if thediameter is large. Therefore, a particular portion of the char motor inthe low velocity section is exposed to a reduced amount of gases incomparison to a particular portion of the char motor in the highvelocity section.

EPDM Composition A was formed into a thin sheet, cured, and assembledinto the char motor by conventional techniques. The thickness of theinsulation was measured at selected intervals, nominally one inch apart,before firing the char motor. The weight of the part was also recordedbefore firing the char motor. After firing, the char motor wasdisassembled, and the thickness and weight of the insulation weremeasured again. The rate at which the insulation is reduced or eroded isexpressed in terms of the reduction of the thickness of the insulationper second, and is referred to as the material affected rate or materialablation rate (“MAR”). The MAR of the insulation was determined bysubtracting the post-fired thickness of virgin insulation (i.e., afterthe char had been removed) at a given point from the pre-fired thicknessat the same point and dividing the result by the burn time of the charmotor. The average weight loss of the insulation was determined as afunction of the pre-fired weight. The MAR and average weight loss areindicators of damage (e.g., ablation) to the insulation, where lowernumbers indicate better insulative and ablative performance. Theablative performance of the insulation is shown in FIGS. 5-7 for the lowvelocity, mid velocity, and high velocity sections of the char motor.

In FIG. 5, the percent weight loss for the insulation formed from theprecursor composition described in Example 1 (identified in FIG. 5 as“EPDM Composition A”) is compared to that of the two conventional,silica-filled EPDM compositions (indicated in FIG. 5 as “EPDMComparative Composition C” and “EPDM Comparative Composition D”). Thepercent weight loss was measured for the low velocity, mid velocity, andhigh velocity sections of the char motor. EPDM Composition A exhibitedimproved or comparable ablative properties compared to the twoconventional, silica-filled EPDM compositions.

In FIG. 6, the MAR for the insulation formed from the precursorcomposition described in Example 1 (identified in FIG. 6 as “EPDMComposition A”) is compared to that of the two conventional,silica-filled EPDM compositions (indicated in FIG. 6 as “EPDMComparative Composition C” and “EPDM Comparative Composition D”). TheMAR was measured for the low velocity, mid velocity, and high velocitysections of the char motor. EPDM Composition A exhibited improved orcomparable ablative properties compared to the two conventional,silica-filled EPDM compositions.

In FIG. 7, the average MAR for the insulation formed from the precursorcomposition described in Example 1 (identified in FIG. 7 as “EPDMComposition A”) is compared to that of the two conventional,silica-filled EPDM compositions (indicated in FIG. 7 as “EPDMComparative Composition C” and “EPDM Comparative Composition D”). Theaverage MAR was measured for the low velocity, mid velocity, and highvelocity sections of the char motor. EPDM Composition A exhibitedimproved or comparable ablative properties compared to the twoconventional, silica-filled EPDM compositions.

While the disclosure may be susceptible to various modifications andalternative forms, specific embodiments have been shown by way ofexample in the drawings and have been described in detail herein.However, it should be understood that the invention is not intended tobe limited to the particular forms disclosed. Rather, the invention isto cover all modifications, equivalents, and alternatives falling withinthe scope of the following appended claims and their legal equivalents.

What is claimed is:
 1. A precursor composition, comprising, beforecuring: ethylene propylene diene monomer (EPDM), zinc oxide, silica, asolid chlorinated paraffin, and a curative.
 2. The precursor compositionof claim 1, wherein the precursor composition comprises from about 4.2parts to about 9 parts of the solid chlorinated paraffin.
 3. Theprecursor composition of claim 1, wherein the precursor compositioncomprises from about 0.35 part to about 0.75 part of the stearic acid.4. The precursor composition of claim 1, wherein the precursorcomposition comprises from about 2.1 parts to about 4.5 parts of thezinc oxide.
 5. The precursor composition of claim 1, wherein theprecursor composition comprises from about 21 parts to about 45 parts ofthe silica.
 6. The precursor composition of claim 1, further comprisingtrimethylolpropane trimethacrylate.
 7. The precursor composition ofclaim 1, wherein the curative comprises a peroxide.
 8. The precursorcomposition of claim 1, wherein the precursor composition comprises lessthan about 12 parts of the curative.
 9. A precursor composition,comprising, before curing: ethylene propylene diene monomer (EPDM), zincoxide, silica, a solid chlorinated paraffin, stearic acid, anantioxidant, a plasticizer, a coagent, and a peroxide.
 10. The precursorcomposition of claim 9, wherein the EPDM comprises a non-conjugateddiene and the EPDM comprises a diene content of from about 1% by weight(wt %) to about 10 wt %.
 11. The precursor composition of claim 9,wherein the EPDM comprises an ethylene content of between about 40 wt %and about 85 wt %.
 12. The precursor composition of claim 9, wherein theantioxidant comprises polymerized 1,2-dihydro-2,2,4-trimethylquinoline.13. The precursor composition of claim 9, wherein the precursorcomposition comprises from about 0.35 part to about 0.75 part of theantioxidant.
 14. The precursor composition of claim 9, wherein theplasticizer comprises a five carbon petroleum hydrocarbon.
 15. Theprecursor composition of claim 9, wherein the precursor compositioncomprises from about 4.2 parts to about 9 parts of the plasticizer. 16.The precursor composition of claim 9, wherein the coagent comprises alow volatility trifunctional monomer.
 17. The precursor composition ofclaim 9, wherein the coagent comprises trimethylolpropanetrimethacrylate.
 18. The precursor composition of claim 9, wherein theprecursor composition comprises from about 5.6 parts to about 12 partsof the coagent.
 19. The precursor composition of claim 9, wherein theperoxide comprises 1,1-di-(t-butylperoxy)-3,3,5-trimethylcyclohexane.20. The precursor composition of claim 9, further comprising multiwalledcarbon nanotubes.
 21. A rocket motor, comprising: a case, an insulationon at least a portion of the case, and a propellant in the case, theinsulation comprising: a reaction product of ethylene propylene dienemonomer (EPDM), zinc oxide, silica, a solid chlorinated paraffin, and acurative.